Do I need to replace my idler pulley, belt tensioner assembly, or both?

My serpentine belt has been noisy for a couple months. Yesterday the belt fell off while driving. I placed the belt back on the pulleys and started the engine, after about 2 minutes the idler pulley flew off. All of the pulleys appear to be in good condition, but in not sure if the belt tensioner assembly needs to be replaced.

6 Answers

From what I read I believe it may not be your belt tensioner, The big
question I have is HOW could your idler pulley fly off??? You might be
dealing with a broken bolt. IF the idler pulley flew off then I would be
looking for a cracked bolt that should be holding it on; which if it is
broken could cause rattling and improper tension which could
seriously affect the whole serpentine belt system. Primarily your alt,
which won't allow you to drive your vehicle. Check the spin of all of
the pulleys, It could also be bearings of your water pump that go out
and kill the pulley's balance and hence tension, followed by all the
belt. But once again I believe you should be looking for a cracked
bolt.

The plastic pulley separated from the bearing of the idler pulley and that seems to be why it flew off. I am going to try replacing that first since it is only one bolt. That way I can see if the tensioner is also part of the problem and not have to risk a good belt since I will be replacing this one anyway. I would replace the tensioner assembly too, but it seems to be a bigger job on this Buick, so I would rather not if it doesn't need it.

All of my options for idler pulleys were the plastic type unfortunately. I just replaced the idler pulley and took it for a test drive. It seemed to run well and it is back to being quiet like it was a few months ago. I plan on replacing my serpentine belt as well, but it doesn't appear that there is anything wrong with the tensioner.

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My serpentine belt has been noisy for a couple months. Yesterday the belt fell off while driving. I placed the belt back on the pulleys and started the engine, after about 2 minutes the idler pulley f...

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